This project uses the NHANES 1999-2004 data on body composition to examine the prevalence of sarcopenia in the U.S. population. We created a new definition of non-sarcopenic adults based on data from normal weight persons aged 20-39 in the U.S. population and used it to explored the prevalence of sarcopenia in persons aged 40 and older. We are particularly interested in the presence of sarcopenia in men and women over age 70. We will consider how the definitions of sarcopenia and myosteatosis are affected by race, ethnicity or weight. It is unclear if one definition of sarcopenia based on body composition alone can describe the association of body composition with disability for very thin and very heavy individuals. This project aims to assist the American Geriatrics Society in creation of a working definition of sarcopenia for geriatric practice.